Russia is “exceptionally aggressive and reckless in the cyber realm” and “no one should underestimate” the threat to Nato, a senior UK minister will warn in a speech on Monday.

Pat McFadden, whose portfolio includes national security, will tell a Nato cybersecurity conference in London that Moscow “won’t think twice about targeting British businesses”, according to excerpts of his address released on Sunday by his ministry.

He will also note that “unofficial hacktivists” given “impunity” by the Kremlin are committing “increasingly frequent, and in some cases, increasingly sophisticated” attacks around the world.

That includes the recent targeting of South Korea “in response to its monitoring of the deployment of North Korean troops” to Russia.

The accusations come as tensions between Russia and the west have escalated dramatically, with Vladimir Putin warning that the war in Ukraine had the characteristics of a “global” conflict.

The growing frictions have sparked fresh unease in London and other western capitals that Putin may step up cyber-attacks and other non-military measures.

“Given the scale of that hostility, my message to members today is clear: no one should underestimate the Russian cyber threat to Nato,” McFadden will say in a speech to the Nato Cyber Defence Conference at Lancaster House, noting “the threat is real”.

“In the last year, both the Russian military and its unofficial army of cybercriminals and hacktivists have not just stepped up their attacks, but widened their targets to a number of Nato members and partners.”

McFadden will warn that Russia has previously targeted the UK’s “media, our telecoms, our political and democratic institutions and our energy infrastructure”.

He is set to say that “Russian state-aligned groups” have taken responsibility for “at least nine separate cyber-attacks of varying severity against Nato states”.

They include “unprovoked attacks against our critical national infrastructure”.

“These groups are unpredictable, they act with disregard for the potential geopolitical consequences, and with just one miscalculation could wreak havoc on our networks.”

The UK minister will “call out” a Russian military unit – dubbed Unit 29155 – that allegedly carried out cyber-attacks in the UK and Europe, according to the Cabinet Office.

Highlighting Russia’s use of cyber-attacks over the course of its nearly three-year war on Ukraine, he will note that the tactics “can turn the lights off for millions of people”.

“It can shut down the power grids. This is the hidden war Russia is waging with Ukraine.”

But he will insist that Britain and western allies are “countering their attacks both publicly and behind the scenes”.

“Be in no doubt: the United Kingdom and others in this room are watching Russia. We know exactly what they are doing.”